The invention is related to a controllable hydraulic vibration absorber for automotive vehicles. It includes a power cylinder whose interior space is subdivided by means of a piston being slidable by a piston rod into a first (piston rod-side) and a second (piston-side) power chamber. A tube is positioned coaxially with said power cylinder, and jointly with the power cylinder defines a connecting duct. An external tube is positioned coaxially with said power cylinder, respectively with said tube, and which jointly with said tube defines a balancing chamber which is partly filled with oil and which is in connection with said first power chamber through said connecting duct and in connection with said second power chamber through a non-return valve. A switching valve is subjected to the pressure existing within the second chamber. A controllable vibration absorber valve which affords variations of the vibration absorbing power, the non-return valve and the switching valve form a valve assembly.
A vibration absorber of this kind is known, for example, from the German patent specification, No. 3,303,293. The two power chambers of the prior-art vibration absorber can be connected to the balancing chamber separately from each other only through a bottom valve which is pressure-dependently controllable so that in the thrust stage it connects the balancing chamber and the first power chamber and in the traction stage exclusively the second power chamber. In this way, in both stages the total displaced vibration absorbing liquid must flow through the vibration absorber piston with a vibration absorbing power adjusting apparatus. In order to actuate the vibration absorbing power adjusting apparatus which is formed by a variable opening, a rotating solenoid is provided at the upper end of the piston rod. A control rod is positioned within the piston rod and includes a disc that can be rotated. In this configuration, the disc interacts with the variable opening whose active diameter is being varied.
The state-of-the-art vibration absorber is less advantageous than the present invention because it requires sophisticated set-up of the vibration absorber piston which has two preadjusted vibration absorber valves and whose manufacture involves considerable costs. Also both the complicated, pressure-controlled switching valve which is positioned at the bottom of the power cylinder and the method of adjustment of the vibration absorbing power is also a disadvantage. The adjustment takes place within the vibration absorber piston and is attained by an interaction of a plurality of electrical and mechanical components.
It is, therefore, the object of the present invention to provide a hydraulic vibration absorber with adjustable vibration absorption of the kind mentioned above which is distinguished by a simpler structure and, thus, low manufacturing cost. In particular the variation of the vibration absorbing power is rendered possible within a wide range with simple-design and reliably functioning components.
According to the invention this object is achieved in that the controllable vibration absorber valve is configured such as to allow a flow through it in one direction only and such as to be integrated as to its action between the connecting duct and the balancing chamber in the valve assembly. The switching valve is inserted between the second power chamber and the connecting duct. Due to this inventive provision, a major simplification of the manufacture is attained making use of a modular concept. A valve assembly so constructed can be manufactured and tested completely separately. The simple design of the vibration absorber piston affords a smooth incorporation of a travel measuring system which is of importance for the regular functioning of the vibration absorber. In addition, the vibration absorber valve which features a unidirectional flow through it will allow it to be optimized with regard to the compensation of the fluid dynamic forces.
According to one embodiment of the invention, the valve assembly is accommodated within a valve housing which is located in the bottom range of the power cylinder. The non-return valve, the switching valve, and the controllable vibration absorber valve are configured so as to be coaxial with respect to one another. Due to the compact design of the vibration absorber, space availability is not a problem.
An extension of the vibration absorber stroke is achieved in a further preferred embodiment of the invention in that the valve assembly is positioned in a valve housing which is provided in the bottom range of the power cylinder and is preferably welded to the external tube. The non-return valve and the switching valve are positioned coaxially with each other and the controllable vibration absorber valve is positioned at a right angle to the axis of the non-return valve, respectively of the switching valve. As a result of this, the influence that the longitudinal acceleration of the vibration absorber has on the closing element of the vibration absorber valve will be greatly reduced.
A particularly simple structure of the inventive vibration absorber is achieved in another advantageous embodiment of the invention in that the non-return valve and the switching valve are configured coaxially with each other at the bottom of the power cylinder. The switching valve is provided between the second power chamber and the connecting duct. The controllable vibration absorber valve allowing a flow through it in one direction only and being inserted as to its action between the connecting duct and the balancing chamber is housed within a vibration absorber valve housing which is separated from the valve housing, at a right angle to the axis of the non-return valve, respectively of the switching valve.
In a further embodiment of the inventive subject matter the controllable vibration absorber valve is constructed so as to be connected to the valve assembly as a separate component. This solution is especially expedient in chassis systems with a level control device, since otherwise the balancing chamber requires too much space at the vibration absorber. In addition, an upside-down incorporation is also possible.
According to another advantageous embodiment of the invention the switching valve, respectively the second non-return valve, is formed by a valve disc which interacts with passages formed in a valve body and which is elastically prestressed. The first non-return valve is designed in the shape of a closing element which interacts with a sealing seat formed in the valve body and which is elastically prestressed. The aim achieved in this manner is that no crossing of the hydraulic pressure agent paths will come about in operation, so that the behavior of the valve assembly can be regarded as non-critical as far as flow resistances are concerned.
A further advantage is achieved in a further embodiment in that the switching valve, respectively the second non-return valve, is formed by a valve disc which is arranged coaxially with the power cylinder. The switching valve interacts with passages formed in the valve housing, is elastically prestressed, and is positioned radially outside the power cylinder. These provisions afford a facilitated routing of lines leading to the travel measuring system and create favorable conditions for the realization of a travel-dependent vibration absorbing function in the bottom range of the hydraulic cylinder.
In an embodiment the invention the above-mentioned travel-dependent vibration absorption both in the traction and in the thrust stage is achieved in that the power cylinder is furnished with openings which can completely or partly be passed over by the piston in its final strokes. The openings are formed in an annular chamber which is defined by the second non-return valve and by the valve housing. This is of particular importance in modern chassis control systems with a semiactive control. A very "smooth" adjustment is customary which results in wide vibration absorber strokes at high speed so that an efficient vibration absorption in the final positions contributes to the protection of the components.
A further increase of the stroke is achieved according to another advantageous feature of the invention in that the non-return valve and the switching valve are formed by valve discs which are positioned outside the power cylinder within a valve housing at a distance from each other coaxially with the power cylinder. They are elastically prestressed and interact with passages formed in a valve body. The controllable vibration absorber valve is positioned within an absorber valve housing which is furnished with hydraulic pressure fluid ducts and is laterally flangeable to the valve housing. The power cylinder is provided with openings in the final stroke positions of the piston which are in active connection with the passages. Possibilities of free access through the bottom of the power cylinder are created by these measures which can, for instance, be made use of in the event of the incorporation of sensors etc. In addition, an easy exchangeability of the vibration absorber valve is safeguarded which will be expedient, in particular, for test purposes and in case of a damage.
In this configuration each one of the valve discs is prestressed by one spiral spring which takes support at the valve housing, respectively at the tube. It is the essential advantage of the spiral springs with low and slight pressure increases in the presence of large flow rates are realized. Furthermore, the arrangement allows for the use of large spiral springs without restriction of the piston stroke.
According to the invention the vibration absorber valve may be designed in the shape of a seat valve or a slide valve whose closing element is actuatable either directly or as a main stage indirectly through a pilot control stage by an electromechanic transducer.
It another advantageous design version the valve housing is designed in two-parts and includes the first valve body and a vibration absorber valve part in whose central range slots are formed, respectively with bores and a central bore. A guided slide serves as a closing element of the vibration absorber valve and is preferably designed so as to be pressure-balanced and is coupled to a second, pressure-unbalanced slide which is guided on the vibration absorber valve part and which interacts with slots, respectively with bores being configurated in the latter.
Especially in the range of small volumetric flow rates these measures bring about an improvement of the functioning, respectively of the behavior of the inventive vibration absorber with regard to desired spring comfort, as beyond an adjustable pressure limiting function the restricting effect, too, allows adjustment by the described valve.
Another advantageous design variant of the invention is that the valve housing is designed in two-parts and is composed of the first valve body and a guide element. The main stage is formed by a main slide which interacts with a control edge formed in the guide element and the pilot control stage is formed by a control slide which interacts with control bores formed in the main slide. A two-stage vibration absorber valve having a set-up of this kind requires less positioning power and affords a better handling of more elevated vibration absorbing forces.
In this context, the control edge is positioned adjacent flow-off bores which are formed in the guide element and are in connection with the balancing chamber and through whose size and geometric shape the performance characteristics of the main stage are influenced. It will be expedient in this conjunction when the main slide is open in its upper part and is furnished with bores which allow it to be brought in connection with said flow-off bores.
According to a further preferred embodiment of the invention the main slide is prestressed by means of a first compression spring in the closing direction of the main stage and is abutted against the first valve body. It is safeguarded in this manner that the main stage is being closed automatically at the standstill of the piston.
Any suction problems, respectively displacement problems at the main slide occurring during operation of the inventive vibration absorber are preferably eliminated when the abutment of the main slide against the first valve body takes place by means of axial projections.
In another advantageous embodiment of the invention, the main slide is provided with restricting bores which end up, on one side, in the range of the bores and, on the other side, in a hydraulic chamber which is defined by the main slide in the guide element. By this provision both a smooth oil supply of the pilot control stage and functionally important pressure drops during the flow through the restricting bores are achieved.
An advantageous coupling of the main stage to the pilot control stage is achieved in another embodiment of the subject matter of the invention in that the control slide is guided in the main slide and may be in abutment against the latter under the prestressing action of a second compression spring.
An especially advantageous embodiment of the invention, whose pilot control stage is electromagnetically actuatable by a plunger coil interacting with a permanent magnet, consists in that the control slide is connected to the plunger coil support by means of a connecting element whose head can be in abutment against the main slide. In this way, an exact control of the vibration absorbing power in the lower range of piston speed and an adjustability of the vibration absorber valve and, thus, variations of the vibration absorbing power are rendered possible. Simultaneously a swinging of the control slide over the control bores is prevented. Of particular advantage, in this context, is the favorable dynamic behavior of the plunger coil.
According to another preferred design variant the electromechanic transducer essentially includes a plunger coil and permanent magnet mounted in a hydraulic chamber which is in connection with the balancing chamber. The end of the connecting element is fixed to the plunger coil support and is subjected to the effect of the pressure existing in the balancing chamber. In this way, the plunger coil is subject only to the pressure in the balancing chamber, whereby simultaneously the effect of a downwardly directed force on the captivating element is attained.
The tube is axially slidingly and/or rotatably positioned on the power cylinder in order to afford ease of assembly, respectively of adjustment of a laterally disposed vibration absorber valve.
In other disclosed versions of the invention, the moving direction of the vibration absorber piston is recognized and a monitoring of the relative speed of movement between the power cylinder and the vibration absorber piston is possible. In this version a flow switch is inserted between the second power chamber and the balancing chamber or a travel sensor is provided which senses the piston stroke.
The travel sensor may, for example, include a pipe, preferably an aluminum pipe, projecting into the piston rod and sealedly guided within the piston, and, by a core movably positioned within the pipe. The pipe partly projects out of the piston rod in the piston range. The pipe is fixed, at its end jutting out, in the range of the valve assembly, while the core is fixed to the piston rod.
According to another design of the travel sensor the pipe is positioned within the piston rod, while the core is sealedly guided within the pipe and is fixed to the bottom of the valve housing.
An improvement, respectively an increase of the responsiveness of the inventive vibration absorber is achieved in a variant in which the travel sensor is integrated in the hollow piston rod. The piston rod is furnished with means which afford a ventilation of its interior space. For this purpose, the sensor core defines, for example, a chamber within the pipe, which is in connection through a third non-return valve with vent ducts in the first power chamber. Furthermore, it will be of advantage when the third non-return valve is preceded by a filter. Along these lines, it will be particularly expedient when the third non-return valve and the filter are accommodated within a threaded plug which caps the piston rod.
According to an advantageous further development of the inventive subject matter the core is tubular in its upper range and jointly with the pipe defines an annular chamber which is in connection with the second power chamber. The annular chamber can be brought into connection with said power chamber through a fourth non-return valve which is formed by a valve slide guided in an elastically prestressed way on the core and interacting with openings which are formed in the core.
A unidirectional volumetric flow through a hydraulic pressure fluid connection within the piston rod is achieved by these provisions. Of course, the fourth non-return valve becomes effective exclusively in the thrust stage, while in the traction stage a return movement of the air which is not dissolved in the hydraulic oil cannot take place on account of the closed non-return valve. The chamber which is defined within the aluminum pipe can, optionally, be brought into connection with the annular chamber through a pressure limiting valve which is preferably constituted by a valve piston which is sealedly guided within the core, which is elastically prestressed and which interacts with openings (bores) formed in the core.
In order, finally, to minimize the pressure drops which occur in the valve assembly, according to another embodiment of the inventive vibration absorber the piston is furnished with a fifth non-return valve which affords a connection between the two power chambers in the event of a pressure increase in the second power chamber.
Further details, features and advantages of the invention will be revealed by the undermentioned description of a total of seven embodiments, making reference to the accompanying drawing.